1. Technical Field of the Invention
The present invention elates to a method of synchronizing reverse links and a transmission method using synchronous reverse links in a radio communication system.
2. Description of the Prior Art
In a typical Code Division Multiple Access (CDMA) communication system, the interference between forward link channels is considerably reduced because forward link channels are identified by different orthogonal channels. In reverse links, the distance between a base station and each mobile station is different from mobile station to mobile station and the propagation time delays of signals from different mobile stations are also different.
Since the cross correlation values of orthogonal codes are much larger than those of Pseudo Noise (PN) codes when the signals are not synchronized with each other, the reverse link channels of Interim Standard-95 (IS-95) are identified by different PN codes. However, if channels can be synchronized with each other in reverse links and the channels are identified by orthogonal codes, the interference between reverse channels can be reduced considerably.
Also, there is a method to synchronize reverse channels where the receiving times of a forward synchronization channel and a reverse synchronization channel (that is, pilot channels) are used to set up synchronization and then synchronization control messages are transmitted through a forward traffic channel to maintain synchronization.
However, in the conventional method as described above, there are some disadvantages that separate synchronization channel establishment is required, the throughput of the traffic channel is degraded, and the transmission of control signals is delayed due to the transmission of the synchronization control messages through the traffic channel.
Therefore, an object of the present invention is to provide a transmission method using synchronous reverse links where a mobile station controls its transmission time to establish reverse link synchronization according to synchronization control messages received through a conventional control channel, and the mobile station controls its transmission time according to synchronization control bits received through a traffic channel of the mobile station.
According to one aspect of the present invention, this and other objects are accomplished by a method of establishing reverse channel synchronization, including the steps of: a) transmitting, from a mobile station, an access signal to a base station through a control channel; b) receiving, at the base station, the reverse access signal, calculating the difference in time between a reference time and the receiving time, generating and transmitting a synchronization control message to the mobile station through a control channel; and c) adjusting, at the mobile station, the reverse transmission time and transmitting a reverse link signal to the base station.
According to another aspect of the present invention, the above and other objects are accomplished by a transmission method using synchronous reverse channels in a wireless communication system, including the steps of a) transmitting, from a mobile station, an access signal to a base station through a control channel; b) receiving, at the base station, the reverse access signal, calculating the difference in time between a reference time and the receiving time, generating and transmitting a synchronization control message to the mobile station through the control channel; c) adjusting, at the mobile station, the reverse transmission time and establishing synchronization by transmitting a reverse link signal to the base station; d) transmitting, from the base station, a traffic channel start command to the mobile station through a traffic channel; e) transmitting, from the mobile station, data to the base station through the traffic channel; D periodically comparing, at the base station, the receiving time with the reference time, generating and transmitting a synchronization control bit to the mobile station through the traffic channel; and g) controlling, at the mobile station, a transmission time according to the synchronization control bit.